Support multiple network interfaces

[mflendrich]

Issue originally authored by tnozicka as #1892

Pods can have more then one network interface:

• https://cloud.google.com/anthos/clusters/docs/bare-metal/latest/how-to/multi-nic
• https://docs.aws.amazon.com/eks/latest/userguide/pod-multiple-network-interfaces.html

It should be possible to configure ScyllaClusters to use different intefaces / IPs for node-to-node, client-to-node and other traffic.

Tasks

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1. Add design doc for configuring specific network intefaces
2. Add CI support for multiple nics
3. Implementation + tests + docs